premature flac decode deletion solved

flac-decoder.rkt

@@ -92,6 +92,15 @@
       )
     )
 
+  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+  ; goal   : Decode FLAC frames and release the decoder on every exit.
+  ; pre    : Handle is open and is not already being read.
+  ; post   : The native decoder is released and reading is false.
+  ; result : Void on completion; decoding and callback errors propagate.
+  ; internals: reader processes frames and callbacks. dynamic-wind deletes
+  ;            the native decoder before clearing reading, so flac-stop
+  ;            cannot return while decoder cleanup is still in progress.
+  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   (define (flac-read handle)
     (let* ((ffi-handler (flac-handle-ffi-decoder-handler handle))
            (state (ffi-handler 'state))
@@ -103,10 +112,14 @@
                          (if (flac-handle-stop-reading handle)
                              (begin
                                (dbg-sound "handling stop at: ~a" (current-milliseconds))
-                               (set-flac-handle-reading! handle #f)
                                'stopped-reading)
                              (let* ((st (ffi-handler 'state)))
-                               (ffi-handler 'process-single)
+                               (when (memq st '(ogg-error seek-error aborted
+                                               memory-allocation-error uninitialized))
+                                 (error 'flac-read "Decoder cannot continue in state ~a" st))
+                               (unless (ffi-handler 'process-single)
+                                 (error 'flac-read "Could not decode FLAC frame ~a (state ~a)"
+                                        frame-nr (ffi-handler 'state)))
                                (unless (eq? state st)
                                  (set! state st)
                                  (dbg-sound "Now in state ~a (frame-nr = ~a) (int-state = ~a)"
@@ -131,14 +144,17 @@
                                  )
                                
                                (if (eq? st 'end-of-stream)
-                                   (begin
-                                     (set-flac-handle-reading! handle #f)
-                                     st)
+                                   st
                                    (reader (+ frame-nr 1))))))
                        ))
-        (reader 0)
-        ; done reading, delete flac encoder
-        (ffi-handler 'delete)
+        (dynamic-wind
+          void
+          (λ () (reader 0) (void))
+          (λ ()
+            (dynamic-wind
+              void
+              (λ () (ffi-handler 'delete))
+              (λ () (set-flac-handle-reading! handle #f)))))
         )
       )
     )
@@ -175,6 +191,14 @@
              (ffi-handler 'seek-to-sample sample)))))
 
   
+  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+  ; goal   : Stop decoding and safely release an idle FLAC decoder.
+  ; pre    : Handle was returned by flac-open.
+  ; post   : Reading and native decoder cleanup have finished.
+  ; result : Void; repeated stops and stops after EOF are harmless.
+  ; internals: An active reader observes stop-reading and owns cleanup.
+  ;            Otherwise the FFI handler performs idempotent deletion.
+  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   (define (flac-stop handle)
     (let ((ct (current-milliseconds)))
       (dbg-sound "requesting stop at: ~a" ct)